a. Field of the Invention
The present invention generally relates to optical systems, and more particularly to detecting contamination within such optical systems.
b. Background of Invention
Optical metrology and inspection equipment such as, for example, reflectometers may often use high power optical lens/objectives in close proximity to surfaces for measurement and/or inspection purposes. In manufacturing environments these surfaces may often release gases or vapors that can coat the lens/objectives in such a manner that light collected by these lens/objectives is distorted and/or attenuated. The measurement and/or inspection results may thus be distorted as a result of the measurement being influenced by the existing contamination.